1. Field of the Invention
The present invention relates to machining by means of oscillatory vibrations and, more particularly, to ultrasonic machining for machining the front surface of a work-piece by means of a tool of which the front surface has a contour complementary to that to be reproduced on the work-piece.
The invention is applicable particularly in the field of manufacture of graphite work-pieces such as electrodes intended to be used as tools for machining by electro-erosion or again in the field of manufacture of moulds for injection moulding of synthetic-resins, ceramics or metal alloys.
2. Summary of the Prior Art
Ultrasonic machining is used more particularly for working on materials such as ceramics, calcined or vitrified materials, graphite and so on which cannot readily be machined by other methods, and has been established as particularly advantageous for reproducing complex profiles which could not be obtained by, for example, electro-erosion or by way of electro-chemical techniques because of the nature of the material to be worked.
However, the possibilities of ultrasonic machining are limited at the present time. In fact, in known machines for ultrasonic machining, the mechanical vibrations are transmitted to the tool by a vibrating part rigid with the tool whilst the work-piece is fixed. The maximum power of existing ultrasonic mechanical vibration generators does not permit the use of tools of large size. In particular, the frontal surface of the tool, which has the relief contours to be reproduced, is limited by the maximum permissible value of the section of the vibrating part. As the relief surface reproduced on the work-piece is at a maximum equal to that of the relief contour present in the front face of the tool, it is not possible to use ultrasonic machining apparatus when the work-piece has relatively large dimensions. In this case it is then necessary to resort to conventional machining methods, such as milling, which renders the operation extremely protracted and delicate, particularly when the contour to be reproduced is complex.
It has already been proposed in U.S. Pat. No. 3,465,480 to effect machining of the front face of a work-piece by means of a fixed tool, the work-piece being secured on a plate movable with an oscillatory movement by means of a mechanical transmission system including eccentrics. However, it is clear that such a system will not allow working with ultrasonic frequency with the advantages of precision and speed which it provides.
The present invention has for its object to provide an ultrasonic machining method which enables the manufacture of relatively large parts and of which use of tools which could not, because of their weight and dimensions, be put into motion to ultrasonic frequencies within reasonable times by means of existing mechanical vibration generators.